PPC just drives traffic to your site - it really doesn't affect SEO rankings. However, if a lot of people go to your site through PPC, find that they really like it, then share the link they found through blogs, social media, social bookmarking, etc...then that will help your SEO. So in that way PPC could indirectly affect your PPC, although you won't get an automatic benefit to SEO ranking just because you're paying for PPC advertising. For SEO, it all comes down to content. If your content is really amazing and worthy of sharing, then you'll start building links virally and you'll see your rankings improved.
Though there's no help with your organic ranking if you run PPC campaign, PPC is worth a try, even when you can have free credit to start Yahoo search marketing in these days.
Getting organic traffic needs efforts and regular work but really its very effective for traffic as well as page rank if you post at some dofollow blogs and forums. It takes some time to get result, but it will give good trraffics if you keep postign at relevant blogs, forums, social book marking sites.